1. Technical Field
The present invention relates to a lighting optical machine and a defect inspection system used for the inspection or observation of critical dimensional pattern defects and foreign matters typically found in manufacturing processes of semiconductor devices or flat panel displays.
2. Background Art
As semiconductors are highly integrated, circuit patterns tend to be finer than ever. Under these circumstances, higher and higher resolution is required for detecting defects of circuit patterns on wafers, which are lithographed through exposure from circuit patterns formed on masks or reticles for use in photolithography processes for manufacturing semiconductors. In order to enhance the resolution, a lighting beam may be changed from visible light to ultraviolet light so that the beam has a shorter wavelength. Conventionally, an Hg lamp has been used as a light source, and among various emission lines generated from an Hg lamp, those with required wavelengths have been optically selected for use. However, the emission lines of the Hg lamp have a broader emission spectrum and it is difficult to correct optical color aberrations thereof. Further, in order to obtain sufficient illuminance, a large light source is necessary, resulting in decreased efficiency.
In recent years, an exposure device carrying a KrF excimer laser with a wavelength of 248 nm as a light source therefor in the semiconductor manufacturing processes has been developed. However, the excimer laser light source is large and predetermined safety measures must be taken due to the use of fluorine gas.
Examples of ultraviolet laser light sources include a laser device wherein the wavelength of a solid-state YAG laser light is converted with a nonlinear optical crystal and an Ar—Kr laser device, and a laser beam with the wavelength of 266 or 355 nm can be obtained thereby. It is advantageous that these laser devices have a larger output power in comparison with lamps conventionally used as light sources, and generate a parallel pencil, the beam passage of which can freely be routed. On the other hand, due to the coherence properties of lasers, laser speckle occurs, and causing adverse influences such as uneven brightness in detecting the circuit patterns formed on a sample. Incidentally, JP Patent Publication (Kokai) No. 2001-141428 A discloses a solution to this problem as a conventional technology. However, the technology of the above publication is not directed at reliability regarding the detection accuracy, such as optical axis adjustment and luminous energy adjustment, or at safety during the use of a laser.